iSyg.] Molecular Physics in High Vacua. 425 
cut out of sheet aluminium, so that the rays from the 
negative pole projected along the tube will be partly inter- 
cepted by the aluminium cross, and will projedt an image 
of it on the hemispherical end of the tube which is phos- 
phorescent. I think you will all now see the shadow of the 
cross On the end of the bulb ( c , d), and notice that the 
cross is black on a luminous ground. Now, the rays from 
the negative pole have been passing by the side of the 
aluminium cross to produce the shadow; they have been 
hammering and bombarding the glass till it is appreciably 
warm, and at the same time they have been producing 
anothei effedt on that glass — they have deadened its sensi- 
bility. The glass has got tired, if I may use the expression, 
by the enforced phosphorescence. Some change has been 
produced by this bombardment which will prevent the glass 
from responding easily to additional excitement ; but the 
part that the shadow has fallen on is not tired — it has not 
been phosphorescing at all and is perfectly fresh ; therefore 
if I throw this star down, — I can easily do so by giving 
the apparatus a slight jerk, for it has been most ingeniously 
construdted with a hinge by Mr. Gimingham, — and so allow 
the rays from the negative pole to fall uninterruptedly on to 
the end of the bulb, you will suddenly see the black cross ( c , d t 
Fig. 9B) change to a luminous one (e, /), because the back- 
Fig. 9 B. 
ground is only faintly phosphorescing, whilst the part which 
had the black shadow on it retains its full phosphorescent 
power. The luminous cross is now dying out. This is a most 
delicate and venturous experiment, and I am fortunate in 
having succeeded so well, for it is one that cannot be re- 
hearsed. After resting for a time the glass seems to 
partly recover its power of phosphorescing, but it is never 
so good as it was at first. 
We have, therefore, found an important fadl connected 
with this phosphorescence. Something is projected from 
the negative pole which has the power of hammering away 
at the glass in front of it, in such a way as to cause it not 
